The present invention generally relates to the art of measurement of gravital fluid flow, and specifically to said measurement by use of electrical capacitance phenomena in conjunction with a channel-choke critical depth meter.
The art of flow measurement of fluids, effluents, liquefied sewage and the like in functional gravital conduits, such as pipelines and sewer lines, is beset with numerous problems. Conventional mechanical meters using articulating floats, probes and vanes are susceptible to clogging by suspended particulate matter. And, most conventional meters require interim stoppage of the flow for placement of the meter in situ even where a spot measurement and no permanent installation is desired. This is because the interior surfaces of the aforementioned conduits, being invariably irregular with protruding mortar, casting flash, and the like, cause disruptive turbulence. Even conventional meters which employ standard Palmer-Bowlus, Parshall, or broad-crested flumes require interim flow interruption to permit said interior surfaces to be smoothed with a filling compound both upstream and downstream of the flume to avoid said turbulence. Thus, both flow interruption and construction effort are necessary.
It is known in the prior art to measure fluid flow in a flume by means of capacitive effect; i.e., deploying a pair of spaced plates within the flume and measuring the capacitive coupling therebetween which is varied by the height of the fluid in the flume. This method has an inherent limitation in that the variation in measured capacitance is slight, and therefor inaccurate. Further, the flowing fluid is relied upon to vary the capacitive coupling. The fluid may be non-homogeneous, causing variations in the capacitive effect and wide fluctuations in the flow measurement. Also, the fluid may be corrosive or may carry particulate matter; in either case the capacitive probes may be altered by the fluid, causing erroneous readings or requiring constant recalibration.